[aka-blackboots]

What

Exact Boolean for a full cylinder minus a half-space cuboid (one face plane cuts the cylinder).

Before, this cut failed when the plane was oblique to the cylinder axis (coverage gap), or parallel to a sloped axis (SSI support residual). Now the kept part is built directly:

• the side, trimmed by the exact cut ellipse (parameter = cylinder angle), or by two rulings when the plane is parallel to the axis;
• full or chord-clipped caps;
• one planar cut face.

Aligned subtractions keep their existing builders.

Robustness

• The chart is built from cross products, so near-perpendicular cuts keep an orthonormal frame.
• The near-parallel guard is a rounding bound on the ellipse centre and amplitude, not an absolute value.
• Only exact results and UnresolvedIntersection replace the original error; other failures keep the generic fallbacks.
• Cuts within 1e-3 r of a side or rim (tessellation slivers) go to the other paths.

Tests

• 9 new crate tests in analytic/booleans/cylinder_half_space.rs (oblique, perpendicular, parallel, sloped axis, near-rim probe families): all pass.
• cargo test --release: 439 pass, 2 fail. The same 2 tests also fail on main at release: 2.0.18 without this change, so they are not caused by it:
  • analytic::tessellation::tests::a_trimmed_curved_face_keeps_its_triangle_set
  • analytic::wasm::tests::text_and_object_tessellation_give_the_pinned_triangles

Files

• main/opengeometry/src/analytic/booleans.rs
• main/opengeometry/src/analytic/booleans/cylinder_half_space.rs (new)